Outdwelling slit valves have been proposed in the past. For example, see U.S. Pat. Nos. 5,201,722 and 5,984,902, which disclose transversely directed disc-shaped slit valve diaphragms each having a central slit, the axial flexural displacement of which is mandatorily constrained by abutment structure fore and/or aft of each transverse disc-shaped diaphragm. Prior outdwelling slit valves leave unanswered problems of interior dead space, provision of greater rates of flow without compromising the level of back pressure, and lack valve integrity.
Outdwelling valves of the type in question have been prone to low flow rates due to the region in which a slit valve can be placed within a disc, for example, and still have enough space to securely hold the disc in position. The placement of the slit valve disc is often unstable, being prone to being dislodged under higher than normal pressures, causing the slit valve to either malfunction or perform poorly. In some outdwelling slit valves the limited space is used to add features like extra valves to work in one direction or the other, which lowers the performance of the valve.